Rolf... Heisenberg's particle ???.. you guys crack me up ! The stiffness you are trying to calculate (who said anything about measuring ?) is nor more or less of a moving target then with a RS&C system. Its just generated by different mechanisms. A CR board in unloaded state have pretty predictable amounts of compression in them. No problem there. The problem seems to be understanding what exactly happens when you load them. I would submit that a good starting place is to view the curve of underside of the unloaded panel as if it was unrestricted by the ribs and figure how much the edge to edge distance would increase if it were flattened thus. Then one has a good idea of how much added compression is created in the panel for any degree of load since since that translates to some specific lessening of its radius. Knowing how much the edge to edge distance would increase if unrestricted yields the amount of compression stress generated in the restricted case. Added to what is already there from the unloaded state and one can figure pretty accurately what amount of compression is in the panel for any given amount of loading. One can easily calculate how much resistance towards bending a given rib has for a given starting point. In a CR board in unloaded state the ribs already stressed and bent in a convex (to the panel) form. Downbearing will exert at least two forces on the ribs.. long the grain axial stress which will tend to bend them further, and a downwards force which will tend towards straightening them out. Since up until the point panel compression failure occurs it is obvious which one of these two wins out.... its just to calculate the net effect of each of these two opposing forces and one should be in the ball park. One other point would which seems to be over looked is the shape (convex or concave) of the rib relative to the panels underside at any given time. But I'll leave that lie for the moment. Heisneberg's Particle indeed... quantum physics like realllly applies here :) Cheers RicB Well put, David. My instinct and experience would lead me to agree. It would sort of be like measuring Heisenberg's particle in that the very stiffness we would try to measure is always changing, just by our very breath as we lean over the thing to examine it. Jude Reveley, RPT Absolute Piano Restoration, LLC Lowell, Massachusetts (978) 323-4545
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